(1) Field of the Invention
The present invention relates generally to acoustic signal generating devices, and more particularly to a mechanical device capable of generating an acoustic signal at a specific depth.
(2) Description of the Prior Art
Acoustic signals in active sonobuoys are produced by an array of active transducers that are driven electronically by means of a signal generator, a power source and an electric driver stage. The power source provides the necessary power to operate the signal generator and the electronic driver. Typically, the power source is a battery. The signal generator produces a specified signal and passes the signal to the driver stage where it is amplified so as to drive the active transducer array. The array produces the acoustic signal which is propagated through the water. Such electronically driven generators are complex, costly and have suffered from being unreliable. A simplified mechanically driven generator can reduce cost and can be made more reliable.
However, prior art mechanical sound generators are also typically complex, often relying on compressed gas or motors to actuate a striker against a plate. For example, U.S. Pat. No. 3,433,202 to Sharp et al. discloses an impact energized sound source which uses compressed gas to propel a striker through an evacuated guide tube and against a radiating plate. U.S. Pat. No. 3,137,835 to Bielecki et al. discloses an underwater mechanical sound generator resulting from the movement of motor driven pistons within the device. U.S. Pat. No. 3,053,220 to Sawyer discloses an underwater impact sound source having a dual spring-loaded impact rod. A free floating striker is attached to the rod while the springs and impact rod are each are mounted on telescoping tubes, all adding to the devices complexity. Also, the Sawyer device makes no provision for actuating the device at a specific depth. Other, similarly complex, and/or non-depth sensitive devices are disclosed by Abrahamsen et al. and Donsky in U.S. Pat. Nos. 3,229,404 and 5,233,570, respectively. In abandoned application Ser. No. 07/904,626, current inventor Sullivan disclosed a mechanical sound generator including a pressure sensitive piston which acted against two rods fixed end to end. The separation of the rods by the piston allowed a spring activated piston to strike a ledge, causing the acoustic signal. As the rods were fixed end to end, there was a distinct possibility that jarring of the device would cause premature actuation, especially as the device may be dropped into the water from a considerable distance. Also, the end to end configuration could lead to assembly problems when trying to align the rod ends.